The assault that began overnight focused on the Shabwa province towns of Maifaa and Azzan, the ministry's 26sep.net news website said.

Three vehicles were destroyed and six suspected militants travelling in them killed, it added.

Residents of the two towns said fierce fighting was continuing on Thursday.

The army launched a major offensive on Tuesday aimed at clearing the jihadists from their remaining strongholds in villages and smaller towns in Shabwa and neighboring Abyan province.

The operation began with a setback for the army when a convoy fell into an Al-Qaeda ambush in which 15 soldiers were killed and 15 more taken prisoner, three of whom were later executed.

So far, a total of 21 soldiers and 21 suspected militants have been reported killed in the ground offensive, which followed intense US and Yemeni air strikes last week.

Al-Qaeda in the Arabian Peninsula -- a merger of the network's Yemeni and Saudi branches -- is regarded by Washington as its most dangerous franchise and has been subjected to an intensifying drone war this year.

The jihadists took advantage of a 2011 uprising that forced veteran strongman Ali Abdullah Saleh from power to seize large swathes of southern and eastern Yemen.

The army recaptured several major towns in 2012 but has struggled to reassert control in rural areas, despite backing from militia recruited among the local tribes.